This invention relates generally to devices, such as mobile terminals, radiotelephones and cellular telephones and, in particular, to techniques for sensing the proximity of a user to the device.
There are many kinds of proximity sensors which are used, for example, as limit switches in various kinds of equipment, or to detect motion of objects relative to each other, as well as for other types of control purposes. Typically, these sensors are based on photoelectric, ultrasonic or capacitive principles.
One example of the use of the proximity detection is related to telephones, in particular (but not exclusively) radiotelephones, such as cellular telephones and personal communicators. A feature known as Integrated HandsFree (IHF) makes it possible to use the phone without holding it on the ear or in the hand. In the handsfree mode the sound pressures produced by the earpiece capsule (which may be thought of as a miniature audio speaker) should be much louder to make far-end speech audible to longer distances. On the other hand, when the phone is used on the ear, the sound pressures should be in a normal range. The problem then is how to detect and switch between these two modes.
Proximity detection solves this problem by detecting when the phone is leaving or approaching the ear. According to this detection information the correct level or processing for the earpiece capsule can be selected. Thus, the proximity detection can make the IHF feature fully automatic.
Proximity sensors can be classified into several major types related to the specific properties used to initiate a controlling action. These include the following: field-based, photoelectric and ultrasonic sensors. Furthermore, there are two types of sensors that use field-based detection methods: inductive and capacitive sensors.
Generally, the photoelectric principle is the most widely used, while the capacitive is the second most widely used for proximity detection purposes. Ultrasounds are used mainly for accurate range detection, and not for simple proximity detection.
In a typical case where there is a need for proximity detection, some type of proximity sensor is required to be installed in the device. However, this involves adding cost, weight, complexity and, typically, an additional power drain to the device.
As can be appreciated, it would be beneficial to provide a method and a system for adding a proximity sensing functionality to a device, wherein no additional equipment or components are required.
It is a first object and advantage of this invention to provide a proximity sensing functionality that may be added to a device without also adding additional equipment or components to the device.
It is another object and advantage of this invention to provide a proximity sensing functionality for a mobile telephone, such as a cellular telephone or a personal communicator, that uses the already existing microphone and speaker components, in conjunction with a suitably programmed data processor.
The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention.
The teachings of this invention provide a method and a system which can be used to detect objects and, more generally, environmental changes near a device, such as a mobile telephone, within which the method and system are embodied. Depending on the purpose of the device the detection information can be used to determine whether there are objects near the device, or if the device has a certain orientation relative its environment, and/or if the device is approaching or leaving a certain orientation. The proximity detection method and system are based on an acoustic principle.
An important feature of the teachings herein is that one may utilize sound (audio) transducers already found in the device to realize the proximity detection function, along with digital signal processing or equivalent means. The audio transducers employed by the invention are preferably those designed for use with human hearing and speaking capabilities in the range of about 20 Hz to about 20 kHz, and need not be specially designed transducers, such as transducers designed for ultrasonic applications above 20 kHz.
That is, the invention can utilize the sound transducers that are already used in the device for speech transmission (output speech and input speech) or for some other purpose. Thus, there is no need for additional sensor elements. Furthermore, if the device can provide digital processing means, such as A/D and D/A converters and a signal processor, the device can be constructed to include the proximity detection function without requiring any additional hardware components. Only a suitable operating program is required to implement the proximity detection function in accordance with these teachings.
Also, and assuming that the sound transducers that are already used in the device are employed, then there is no need to redesign the device""s enclosure, and no extra space is required.
The proximity sensing can be done in parallel with the ordinary use of transducers. In this case the transducers are in use already, and the additional power required to implement the proximity sensing function is minimal.
Furthermore, if the sensor somehow fails, the resulting sensing result is that there is an object in close proximity. For example, if the sensing is used with the IHF function, the phone remains in the handset mode and there is no possibility that high sound pressures will be generated near the user""s ear. If the earpiece sensor element fails, then there is clearly no possibility to generate excessive sound pressure near the user""s ear. Further, the sensing algorithm can detect if one of the sensors have failed.
The method is based on a measurement signal that drives the acoustical transducer in the application device. The other transducer in the application device monitors the measurement signal. Any objects near the device alter the measurement signal in a certain way, and these alterations indicate if there are objects near or on the device.
Disclosed herein is a method and a device for detecting if an object is in proximity to the device. The method includes steps of generating a measurement signal; driving an output acoustic transducer of the device with the measurement signal; monitoring an input acoustic transducer of the device to detect the measurement signal; and determining that an object is in proximity to the device based on a detected alteration of the measurement signal. The device may comprise a mobile telephone, such as a cellular telephone, or a personal communicator.
When the device comprises a mobile telephone, the step of determining can be used to verify that a handsfree mode of operation can be entered, and/or to set a volume of a signal driving a speaker, and/or to select, modify, or tune an audio processing technique. The step of determining can also be used to automatically enter a handset mode of operation from a handsfree mode of operation.
In a presently preferred embodiment of this invention the steps of monitoring and determining include steps of operating plural adaptive filters in parallel on the same input signal, with different step sizes, for generating first and second impulse response estimates, respectively, and comparing a difference between the first and second impulse response estimates to a threshold.
In the device a monitoring unit and a determining unit include a decimator for decimating a measurement signal received from a microphone; an anti-comb filter for enhancing the signal to noise ratio (SNR) of the received measurement signal; first and second adaptive filters operated in parallel on the filtered measurement signal, with different step sizes, for generating first and second impulse response estimates, respectively; and a comparator for comparing a difference between the first and the second impulse response estimates to a threshold.